Relationships marked

I've one question.
There are some relationships marked by a white circle and others marked by a blue circle. I tried to understand the meaning of this properties with any success.
Can anyone help me?

for an easier comprehension i attack a picture of the problem i'm asking for

thanks in advance,

Hi Lasly,

The blue color in the circle doesn’t have any special meaning. You can color any circle by any color you like. Just right click on the relationship select “Format…” and change the “Brush Color” to the color you like.